Fiber-reinforced composite material

ABSTRACT

A fiber-reinforced composite material superior in mechanical strength, heat resistance and hot water resistance is provided herein. This composite material is composed of a matrix of a cured product of a resin composition containing as essential components an epoxy resin (A) and an imide compound (B) represented by the following general formula (I), ##STR1## wherein X represents --NH 2  group and/or --OH group, Ar represents an aromatic residue, R 1  represents a hydrogen atom or an alkyl group having from 1 to 10 carbon atoms, R 2  represents a hydrogen atom, an alkyl or alkoxy group having from 1 to 20 carbon atoms or a hydroxyl group, and each of m and n cannot be 0 at the same time, and a fiber (C) as a reinforcing material.

The present invention relates to a fiber-reinforced composite materialsuperior in mechanical strength, heat resistance and hot waterresistance.

Composite materials with fibers as a reinforcing material have a largetensile strength and a large modulus of elasticity, and they are findingextending uses as structural materials for airplanes and automobiles,component parts of engines, sporting goods, goods for leisure timeamusement, etc.

For a material for the matrix phase of these composite materials,thermosetting resins, particularly epoxy resins have mainly been used interms of moldability and mechanical properties.

In recent years, however, with extension of the application field ofcomposite materials, materials have come to be desired which have moreimproved mechanical strength than they have had before and maintainchemical stability and mechanical properties even under severeenvironments such as environments of higher temperature and higherhumidity than in the conventional environments of use.

In fiber-reinforced composite materials, in order that the reinforcingfiber may exhibit its characteristics to the maximum, a resin used as amatrix is important. In order to answer the above demand, improvement inthe matrix resin is necessary.

An object of the present invention is to provide a composite materialsuperior in mechanical strength, heat resistance and hot waterresistance.

The present invention provides a fiber-reinforced composite materialcomprising a matrix composed of a cured product of a resin compositioncontaining as essential components an epoxy resin (A) and an imidecompound (B) represented by the following general formula (I), ##STR2##wherein Ar represent an aromatic residue, R₁ represents a hydrogen atomor an alkyl group having from 1 to 10 carbon atoms, R₂ represents ahydrogen atom, an alkyl or alkoxy group having from 1 to 20 carbon atomsor a hydroxyl group, X represents an --NH₂ group and/or --OH group, andeach of m and n represents a number of from 0 to 30, preferably from 0to 8, more preferably from 0 to 4, provided that m and n are not zero atthe same time, and a fiber (C) as a reinforcing material.

As a result of a study in view of the above situation, the presentinventors have found that a fiber-reinforced composite material obtainedwith the aforementioned epoxy resin composition as a matrix phase and afiber as a reinforcing material is superior in mechanical strength, heatresistance and hot water resistance. The present invention has beencompleted in this way.

The present invention will be illustrated in more detail.

The epoxy resin (A) used in the present invention is a compound havingtwo or more epoxy groups in the molecule. Examples of the epoxy resininclude glycidyl ether compounds derived from dihydric or more phenols[e.g. bisphenol A, bisphenol F, hydroquinone, resorcinol,phloroglucinol, tris(4-hydroxyphenyl)methane,1,1,2,2-tetrakis(4-hydroxyphenyl)ethane] or halogenated bisphenols e.g.tetrabromobisphenol A); novolak type epoxy resins derived from novolakresins which are reaction products of phenols (e.g. phenol, o-cresol)with formaldehyde; amine type epoxy resins derived from aniline,p-aminophenol, m-aminophenol, 4-amino-m-cresol, 6-amino-m-cresol,4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane,4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether,1,4-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene,1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene,2,2-bis(4-aminophenoxyphenyl)propane, p-phenylenediamine,m-phenylenediamine, 2,4-tolylenediamine, 2,6-tolylenediamine,p-xylylenediamine, m-xylylenediamine, 1,4-cyclohexane-bis(methylamine),1,3-cyclohexane-bis(methylamine),5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane,6-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, etc.; glycidyl estercompounds derived from aromatic carboxylic acids (e.g. p-oxybenzoicacid, m-oxybenzoic acid, terephthalic acid, isophthalic acid); hydantointype epoxy resins derived from 5,5-dimethylhydantoin, etc.; alicyclicepoxy resins such as 2,2'-bis(3,4-epoxycyclohexyl)propane,2,2-bis[4-(2,3-epoxypropyl)cyclohexyl]propane, vinylcyclohexene dioxide,3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, etc.; andother compounds such as triglycidyl isocyanulate,2,4,6-triglycidoxy-S-triazine, etc. These epoxy resins may be used aloneor in combination.

Next, the imide compound (B) will be illustrated.

Referring more particularly to Ar in the foregoing formula (I), Ar is amononuclear or polynuclear divalent aromatic residue of which thearomatic ring may or may not be substituted with a lower alkyl group, ahalogen atom, a lower alkoxy group, etc. Specifically, one or more ofaromatic amine residues may be given as Ar. More specifically, when theterminal group X is --NH₂, Ar is an aromatic diamine residue, and whenthe terminal group X is --OH, Ar adjacent to the terminal group is anaminophenol residue and other Ars are an aromatic diamine residue.

For examples of the aromatic diamine there may be given one or more of4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane,4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether,4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl sulfone,3,3'diaminodiphenyl sulfone, 2,4-tolylenediamine, 2,6-tolylenediamine,m-phenylenediamine, p-phenylenediamine, benzidine, 4,4'-diaminodiphenylsulfide, 3,3'-dichloro-4,4'-diaminodiphenyl sulfone,3,3'-dichloro-4,4'-diaminodiphenylpropane,3,3'-dimethyl-4,4'-diaminodiphenylmethane,4,4'-methylene-bis(2-ethyl-6-methylaniline),4,4'-methylene-bis(2,6-diethylaniline),4,4'-methylene-bis(2,6-diisopropylaniline), 4,4'-methylene-bis(2-isopropyl-6-methylaniline), 3,3'-dimethoxy-4,4'diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl,1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene,1,4-bis(4-aminophenoxy)benzene, 2,2-bis(4-aminophenoxyphenyl)propane,4,4'-bis 4-aminophenoxy)diphenyl sulfone,4,4'-bis(3-aminophenoxy)diphenyl sulfone,9,9'-bis(4-aminophenyl)fluorene,3,3'-dicarboxy-4,4'-diaminodiphenylmethane, 2,4-diaminoanisole,bis(3-aminophenyl)methylphosphine oxide, 3,3'-diaminobenzophenone,o-toluidine sulfone, 4,4'-methylene-bis-o-chloroaniline,tetrachlorodiaminodiphenylmethane, m-xylylenediamine, p-xylylenediamine,4,4'-diaminostilbene, 5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane,6-amino-1-(4'-aminophenyl)1,3,3-trimethylindane,5-amino-6-methyl-1-(3'-amino-4'-methylphenyl)1,3,3-trimethylindane,7-amino-6-methyl-1-(3'-amino-4'-methylphenyl)1,3,3-trimethylindane,6-amino-5-methyl-1-(4'-amino-3'-methylphenyl)1,3,3-trimethylindane,6-amino-7-methyl-1-(4'-amino-3'-methylphenyl)1,3,3-trimethylindane, etc.

On the other hand, for examples of the aminophenol, there may be givenone or more of o-aminophenol, m-aminophenol, p-aminophenol,6-amino-m-cresol, 4-amino-m-cresol,2,2-(4-hydroxyphenyl-4-aminophenyl)propane,2,2-(4-hydroxyphenyl-2'-methyl-4'-aminophenyl)propane,2,23-methyl-4-hydroxyphenyl-4'-aminophenyl)propane, 3-amino-1-naphthol,8-amino-2-naphthol, 5-amino-1-naphthol, 4-amino-2-methyl-1-naphthol,etc.

R¹ and R² are as defined above, and R¹ is preferably an alkyl grouphaving from 1 to 10 carbon atoms, more preferably an alkyl group havingfrom 1 to 3 carbon atoms. R₂ is preferably a hydrogen atom, an alkyl oralkoxy group having from 1 to 20 carbon atoms or a hydroxyl group, morepreferably a hydrogen atom, an alkyl or alkoxy group having from 1 to 5carbon atoms or a hydroxyl group.

A method to produce the functional group-terminated imide compound (B)of the present invention will be illustrated.

Those in which X in the formula (I) is --NH₂ may be synthesized byreacting an excess of the foregoing aromatic diamine with a compoundrepresented by the general formula, ##STR3## wherein R₁ and R₂ are asdefined above, (hereinafter referred to as B₁, and the isomers arereferred to as component X and component Y, respectively) according tothe common imidation technique. The compound thus synthesized is takenas B₂.

Those in which X in the formula (I) is --OH may be synthesized by addingthe foregoing aromatic monoamine having an --OH group and aromaticdiamine to B₁ so that the molar ratio of the aromatic diamine to B₁ is(m+n) to (m+n+1), and besides the molar ratio of the aromatic monoamineto B₁ is 2 to (m+n+1) (wherein m and n are as defined above), andcarrying out reaction according to the common imidation technique.

A method to synthesize the functional group-terminated imide compound ofthe present invention has been illustrated above, but the method is notof course limited thereto.

B₁ can be synthesized by the known method. For example, B₁ is obtainedby reacting a compound represented by the general formula, ##STR4##wherein R₁ and R₂ are as defined above, (hereinafter referred to as B₃)with maleic anhydride at a former to latter molar ratio of 1 to 2 in theabsence of a radical polymerization catalyst and in the presence orabsence of a radical polymerization inhibitor. Examples of B₃ includeone or more of styrene, α-methylstyrene, α,p-dimethylstyrene,α,m-dimethylstyrene, isopropylstyrene, vinyltoluene,p-tert-butylstyrene, p-isopropenylphenol, m-isopropenylphenol,1-methoxy-3-isopropenylbenzene, 1-methoxy-4-isopropenylbenzene,vinylxylene, etc.

The functional group-terminated imide compounds of the present inventionthus obtained are soluble in high concentrations in low-boiling solventssuch as acetone, methyl ethyl ketone, methyl isobutyl ketone, methylcellosolve, ethyl cellosolve, methylene chloride, chloroform, etc, andalso they are superior in compatibility with epoxy resins.

The resin composition of the present invention contains theaforementioned epoxy resin and functional group-terminated imidecompound as essential components, and if necessary, it may contain otheradditives such as the known epoxy resin curing agents, curingaccelerators, fillers, flame retardants, reinforcing agents,surface-treating agents, pigments, etc.

The known epoxy resin curing agents include amine type curing agentssuch as aromatic amines (e.g. xylylenediamine) and aliphatic amines,polyphenol compounds such as phenol novolak and cresol novolak, acidanhydrides, dicyandiamide, hydrazide compounds, etc. As to theproportion of the epoxy resin (A) and functional group-terminated imidecompound (B), the sum of (B) and other curing agents is from 0.8 to 1.2gram equivalent per 1 gram equivalent of (A), and preferably the amountof (B) is 0.02 gram equivalent or more per 1 gram equivalent of thesame.

The curing accelerators include amines [e.g. benzyldimethylamine,2,4,6-tris(dimethylaminomethyl)phenol, 1,8-diazabicycloundecene],imidazole compounds (e.g. 2-ethyl-4-methylimidazole), boron trifluorideamine complexes, etc.

The fiber used as a reinforcing material in the present inventionincludes inorganic or organic fibers having a tensile strength of 0.5GPa or more and a Young's modulus of elasticity of 50 GPa or more suchas carbon fibers, graphite fibers, glass fibers, silicon carbide fibers,alumina fibers, titania fibers, boron nitride fibers, aromatic polyamidefibers, aromatic polyester fibers, polybenzimidazole fibers, etc. Thesefibers may be used in the form of continuous tow, woven fabric, shortfiber, whisker, etc.

Also, depending upon the object of use, two or more kinds of fiber orfibers of different forms may be used in combination. Further,incorporating the granular products of talc, mica, calcium carbonate,alumina hydrate, silicon carbide, carbon black, silica, etc. in additionto the reinforcing fiber is also effective to improve the viscosity ofthe resin composition, thereby facilitating molding of the compositematerial, or to improve the mechanical properties such as compressionstrength, etc. of the composite material obtained.

For a method to produce the composite material, any of theconventionally known methods for producing fiber-reinforced compositematerials with an epoxy resin as a matrix, for example a prepreg method,filament winding method, resin injection molding method, etc. can beused, but the prepreg method is suitable. The term "prepreg" referred toherein means reinforcing fibers impregnated with a resin composition,and the prepreg may take any form of sheet, continuous tow, strand, yarnand pellet. The sheet-form prepreg takes a form in which reinforcingfibers have been drawn out in the form of continuous tow, a form inwhich short fibers have been tangled in the form of mat, or a form ofwoven fabric. Also, laminated sheet-form prepregs in which severalpieces of sheet different in structure have been piled up, and those inwhich several pieces of continuous tow prepreg have been bundled, are auseful material.

The fiber content of these prepregs is generally from 5 to 70% byvolume, particularly preferably from 10 to 60% by volume.

After laminating or winding these prepregs into a desired form, bycuring the resin composition by applying heat and pressure, afiber-reinforced composite mateiial can be obtained.

The fiber-reinforced composite material of the present invention issuperior in mechanical strength, heat resistance and hot waterresistance, and useful as a structural material.

The present invention will be illustrated in more detail with referenceto the following examples.

Hereupon, the followings were synthesized as a material for synthesizingthe functional group-terminated imide oligomer by the method givenabove. ##STR5##

REFERENCE EXAMPLE 1

To a flask equipped with a stirrer, thermometer and separater were added29.7 g (0.15 mole) of 4,4'-diaminodiphenylmethane and 242 g of m-cresol,and after dissolving the diaminodiphenylmethane, 48.5 g of xylene wasadded. The temperature was raised to 120° C. At this temperature, 31.4 g(0.1 mole) of Component X was added, and after raising the temperatureto 175° C., dehydration was continued for 5 hours. After completion ofthe reaction, the reaction solution was poured into a hexane/isopropanolmixed solvent, and formed precipitates were filtered, washed twice withthe same solution and dried under reduced pressure to obtain an imidecompound. The melting point of this compound was about 240° C., and theamine equivalent thereof was 643 g/eq.

REFERENCE EXAMPLE 2

An imide compound was obtained in the same manner as in Referenceexample 1 except that 29.7 g (0.15 mole) of 4,4'-diaminodiphenylmethanewas replaced by 24.4 g (0.2 mole) of 2,4-tolylenediamine. The meltingpoint of this compound was about 220° C., and the amine equivalentthereof was 353 g/eq.

REFERENCE EXAMPLE 3

To a flask equipped with a stirrer, thermometer and separater were added80.2 g (0.27 mole) of m-aminophenol and 312 g of mm-cresol, and afterdissolving m-aminophenol, 62.2 g of xylene was added. The temperaturewas raised to 120° C. At this temperature, 110 g 0.35 mole) of ComponentX was added, and an imide compound was obtained by the same procedure asin Reference example 1. The melting point of this compound was 300° C.,and the hydroxyl equivalent thereof was 239 g/eq.

REFERENCE EXAMPLE 4

In the same manner as in Reference example 3, 64 g (0.20 mole) ofComponent X and 230.2 g of m-cresol were charged, and after dissolvingComponent X, the temperature was raised to 70° C.; at this temperature,12.4 g (0.1 mole) of 2,4-tolylenediamine was added, and aftermaintaining the temperature for 1 hour, 22.2 g (0.20 mole) ofm-aminophenol was added; after maintaining the temperature for further 1hour, 46 g of xylene was added, the temperature was raised to 175° C.,and dehydration was continued for 5 hours. Thereafter, an imide compoundwas obtained by the same procedure as in Reference example 3. Themelting point of this compound was 260° C., and the hydroxyl equivalentthereof was 426 g/eq.

REFERENCE EXAMPLE 5

To a flask equipped with a stirrer, thermometer and separater were added26.2 g (0.215 mol) of 2,4-tolylenediamine and 117 g of m-cresol, andafter raising the temperature to 70° C. to dissolve 2,4-tolylenediamine,20.3 g (0.064 mole) of Component X and 24.7 g (0.079 mole) of ComponentY were charged to form a polyamide acid. Thereafter, 25.2 g of toluenewas added, and after raising the temperature to 150° C., dehydration wascontinued at the same temperature for 10 hours. After completion of thereaction, the resin solution obtained was poured into 750 g ofisopropanol, and formed precipitates were filtered off, washed twice anddried under reduced pressure to obtain an imide compound. The meltingpoint of this compound was 260° C., and the amine equivalent thereof was498 g/eq.

REFERENCE EXAMPLE 6

To a flask equipped with a stirrer, thermometer and separater were added20.3 g (0.064 mole) of Component X, 24.7 g (0.079 mole) of Component Y,161 g of m-cresol and 8.68 g (0.0714 mole) of 2,4-tolylenediamine, andreaction was carried out at a temperature of 70° C. for 1 hour.Thereafter, 32.2 g of xylene was charged, and dehydration was continuedat a temperature of 170° C. for 6 hours.

After completion of the reaction, 550 g of the resulting resin solutionwas poured into isopropanol, and formed precipitates were filtered off,washed twice and dried under reduced pressure to obtain an imidecompound. The hydroxyl equivalent of this compound was 473 g/eq, and themelting point thereof was 270° C.

REFERENCE EXAMPLE 7

An imide compound was obtained in the same manner as in Referenceexample 6 except that the amount of Component X was changed to 5.4 g(0.024 mole), that of Component Y was changed to 26.6 g 0.119 mole),8.68 g (0.071 mole) of 2,4-tolylenediamine was replaced by 12 g (0.064mole) of 4,4'-diaminodiphenylmethane and the amount of m-aminophenol waschanged from 15.5 g (0.14 mole) to 8.30 g (0.076 mole). The hydroxylequivalent of this compound was 702 g/eq, and the melting point thereofwas about 270° C.

REFERENCE EXAMPLE 8

An imide compound was obtained in the same manner as in Referenceexample 5 except that 29.7 g (0.094 mole) of Component X and 15.3 g(0.049 mole) of Component Y were charged. The amine equivalent of thiscompound was 506 g/eq, and the melting point thereof was about 260° C.

EXAMPLES 1 to 4

Sumi® epoxy ELA-128 (bisphenol A type epoxy resin having an epoxyequivalent of 187 g/eq; product of Sumitomo Chemical Co., Ltd.) and theimide compounds obtained in Reference examples 1, 2, 5 and 7 wereblended in proportions shown in Table 1 and dissolved in acetone toobtain about 50% by weight resin solutions. These resin solutions weretaken as a resin solution for prepreg.

A carbon fiber (Magnamite® AS 4; product of Sumika Hercules Co., Ltd.)was passed through said resin solution for prepreg to impregnate it withthe resin and rolled round a silicon release paper, as previously woundon a drum, from one side to the other side of the drum while moving thedrum. The amount of the resin attached to the carbon fiber was regulatedby passing the fiber between two stainless steel rods freely adjustablein a gap therebetween. The resulting roll of fiber round the siliconrelease paper was cut across the surface of the drum and removed fromthe drum to obtain a carbon fiber sheet. This sheet was placed for 30minutes in an explosion-proof hot air oven previously set to atemperature of 120° C. to carry out solvent removal and B-stage which ispre-treatment for the complete curing of the resin impregnated into thefiber. The carbon fiber sheet thus prepared was taken as a prepreg.Every prepreg thus obtained contained about 35% by weight of the resinand its fiber weight was 150 g/m². The prepreg was cut, laminated andmatched die molded by means of a hot press. The temperature of the moldwas adjusted to 180° C. Thereafter, the molded product was taken off themold and cured at a temperature of 200° C. in 4 hours to obtain aunidirectional composite material containing 60% by volume of the carbonfiber. The samples thus obtained were measured for mechanicalproperties. The results are shown in Table 1.

COMPARATIVE EXAMPLE 1

A one-way reinforced composite material was obtained in the same manneras in Example 1 except that 30 g of Sumicure® S (diaminodiphenylsulfone; product of Sumitomo Chemical Co., Ltd.) was used in place ofthe imide compound obtained in Reference example 1. The sample thusobtained was measured for mechanical properties. The results are shownin Table 1.

                                      TABLE 1                                     __________________________________________________________________________                                Example                                                                       Example                                                                            Example                                                                            Example                                                                            Example                                                                            Comparative                                               1    2    3    4    example                       __________________________________________________________________________                                                    1                             Composition                                                                          Sumi ® epoxy ELA-128 (g)                                                                       100  100  100  100  100                                  Imide compound in Reference example 1 (g)                                                          136  --   --   --   --                                   Imide compound in Reference example 2 (g)                                                          --   75   --   --   --                                   Imide compound in Reference example 5 (g)                                                          --   --   105  --   --                                   Imide compound in Reference example 8 (g)                                                          --   --   --   107  --                                   Sumicure ® S (g) --   --   --   --   26                            Mechanical                                                                           Interlaminar shear                                                                       Room temperature                                                                        12.5 11.9 12.8 12.2 9.3                           properties                                                                           strength (kg/mm.sup.2)                                                                   120° C.                                                                          6.0  6.2  6.1  6.3  4.0                           of composite      120° C. (wet)*                                                                   4.3  4.1  4.5  4.2  2.1                           material                                                                             0° Flexural                                                                       Room temperature                                                                        210  213  221  216  214                                  strength   120° C.                                                                          138  143  140  138  100                                  (kg/mm.sup.2)                                                                            120° C. (wet)*                                                                   113  117  116  115  66                                   90° Flexural                                                                      Room temperature                                                                        12.5 12.1 13.0 12.4 10.1                                 strength (kg/mm.sup.2)                                                 __________________________________________________________________________     Measuring method:                                                             Interlaminar shear strength . . . according to ASTM D2344                     Flexural strength . . . according to ASTM D790                                *Measurement value after dipping in boiling water for 48 hours.          

EXAMPLES 5 to 9

Sumi® epoxy ELM-434 (tetraglycidyldiaminodiphenylmethane having an epoxyequivalent of 120 g/eq; product of Sumitomo Chemical Co., Ltd.), theimide compounds obtained in Reference examples 2, 3, 4, 6 and 7 andSumicure® M (diaminodiphenylmethane; product of Sumitomo Chemical Co.,Ltd.) were blended in proportions shown in Table 2 and dissolved inacetone to obtain about 50% by weight resin solutions. These resinsolutions were taken as a resin solution for prepreg.

In the same manner as in Example 1, prepregs were prepared, molded andcured to obtain unidirectional composite materials containing 60% byvolume of the carbon fiber, and the mechanical properties of thematerials were measured. The results are shown in Table 2.

COMPARATIVE EXAMPLE 2

100 Grams of Sumi® epoxy ELM 434 (same as in Example 3( and 40 g ofSumicure® S (same as in Comparative example 1) were dissolved in 150 gof acetone to obtain a uniform solution. Using this resin solution, afiber-reinforced composite material was obtained in the same manner asin Example 1, and the mechanical properties of the material weremeasured. The results are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                                 Example                                                                       Example                                                                            Example                                                                            Example                                                                             Example                                                                            Example                                                                            Comparative                                         5    6    7     8    9    example                __________________________________________________________________________                                                           2                      Composition                                                                          Sumi ® epoxy ELM 434 (g)                                                                        100  100  100   100  100  100                           Imide compound in Reference example 2 (g)                                                           100  --   --    --   --   --                            Imide compound in Reference example 3 (g)                                                           --   100  --    --   --   --                            Imide compound in Reference example 4 (g)                                                           --   --   100   --   --   --                            Imide compound in Reference example 6 (g)                                                           --   --   --    100  --   --                            Imide compound in Reference example 7 (g)                                                           --   --   --    --   100  --                            Sumicure ® M (g)  5    11   20    21   24   --                            Sumicure ® S (g)  --   --   --    --   --   40                     Mechanical                                                                           Interlaminar shear                                                                       Room temperature                                                                         13.2 12.9 13.3  13.0 12.7 12.5                   properties                                                                           strength (kg/mm.sup.2)                                                                   120°  C.                                                                          9.0  9.1  8.7   8.9  9.0  8.3                    of composite      120° C. (wet)*                                                                    7.0  6.3  6.5   6.2  6.8  3.1                    material          180° C.                                                                           7.2  7.7  7.6   7.5  7.6  5.6                           0° Flexural                                                                       Room temperature                                                                         215  221  213   206  218  213                           strength (kg/mm.sup.2)                                                                   120° C.                                                                           173  175  171   176  171  149                                      120° C. (wet)*                                                                    148  139  145   142  139  109                                      180° C.                                                                           166  156  152   168  161  128                    __________________________________________________________________________     Measuring method: Same as in Table 1.                                         *Same as in Table 1                                                      

What is claimed is:
 1. A fiber-reinforced composite material comprisinga matrix of a cured product of a resin composition containing asessential components an epoxy resin (A) and an imide compound (B)represented by the following general formula (I), ##STR6## wherein Xrepresents --NH₂ group and/or --OH group, Ar represents an aromaticresidue, R₁ represents a hydrogen atom or an alkyl group having from 1to 10 carbon atoms, R₂ represents a hydrogen atom, an alkyl or alkoxygroup having from 1 to 20 carbon atoms or a hydroxyl group, and each ofm and n represents a number of from 0 to 30, provided that m and ncannot be 0 at the same time, and a fiber (C) as a reinforcing material.2. A fiber-reinforced composite material according to claim 1 wherein R₁in the formula for the imide compound (B) is an alkyl group having from1 to 10 carbon atoms.
 3. A fiber-reinforced composite material accordingto claim 1 wherein X in the formula for the imide compound (B) is --NH₂group.